Research subject: The formulation of sublimation inkjet inks based on disperse dyes requires precise control of dispersion stability and rheological behavior to achieve consistent print quality and printer compatibility. One of the main challenges in this field is establishing an appropriate balance between polymeric dispersants and low-molecular-weight surfactants to prevent sedimentation, viscosity fluctuations, and surface tension instability. This study investigates the influence of nonionic surfactant concentration on the physical characteristics, dispersion stability, and rheological behavior of Disperse Blue 359 in aqueous sublimation inkjet ink formulations.
Research approach: Dye concentrates were prepared using a jar mill in the presence of a polymeric dispersant, glycerol, and deionized water. The concentration of the nonionic surfactant was varied from 0 to 7.1 wt%. The samples were characterized in terms of color strength by UV-vis spectrophotometry, particle size by dynamic light scattering, surface tension by the Wilhelmy method, and rheological behavior by a rotational rheometer. Dispersion stability was also monitored by turbidity measurements over different time intervals.
Main results: The results revealed that the simultaneous presence of the polymeric dispersant and the nonionic surfactant significantly improved the stability and flowability of the system. Specifically, the sample with the optimally concentrated surfactant exhibits turbidity oscillation of less than 30 NTU and a viscosity below 8.5 cp, while the surfactant-free sample experiences a turbidity reduction exceeding 500 NTU over the test duration and a viscosity above 17 cp. At an optimal surfactant concentration of approximately 3.6 wt%, the particle size reached its minimum, color strength reached its maximum, and dispersion stability was maximized. Conversely, both higher and lower surfactant concentrations led to particle aggregation, increased turbidity, and diminished print quality. These findings highlight the critical importance of accurately tuning the ratio of surfactant to dispersant in designing reliable sublimation inkjet inks with desirable optical and rheological properties.